A conventional electronic drive lock is described in German publication "mot", February 1995, pages 102-106. Such a conventional drive lock is based on an access device in the form of an ignition key, a handheld transmitter (or a chip card), a control unit containing the drive lock, and an engine management control unit for controlling a gasoline or diesel engine. Other functional elements present in the vehicle can also be connected to the drive lock control unit, for example the electric fuel pump or the starter. A prerequisite for providing a vehicle equipped with the drive lock as described is that a prescribed unlocking code should be delivered to the drive lock control unit. Because the vehicle cannot, for this reason, readily be started up by an unauthorized person, the conventional drive lock offers at least some protection against theft, i.e. the vehicle being driven away. Given the increasing professionalism of vehicle thieves, however, it is foreseeable that vehicles will be misappropriated by replacing the original, locked drive lock control unit with an unlocked but otherwise functionally identical replacement control unit.
Accordingly, it is the object of the invention to indicate a possibility for preventing the theft of vehicles by replacing a control unit.